Recovery of heavy oil by steam injection



March 12, 1968 A. SATTER ETAL 3,372,750

RECOVERY OF HEAVY OIL BY STEAM INJECTION Filed Nov. 19, 1965 5Sheets-Sheet 1.

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liq-J STEAM INJECTION WELL 4820 0 STEAM INJECTION ST OIL PRODUCING WELL44 Angie? ABDUS SATTER LLOYD E. ELKINS INVENTORS:

ATTORNEY March 12, 1968 A. SATTER ETAL RECOVERY OF HEAVY OIL BY STEAMINJECTION Filed Nov. 19, 1965 5 Sheets-Sheet C5 Z S 5 OIL SAND OIL SANDA: 52 4 SHAL 54f 1 WATER SAND WATER SAND ABDUS SATTER LLOYD E.

ELKINS INVENTORS:

ATTOR/V f March 12, 1968 A. SATTER ETAL 3,372,750

RECOVERY OF HEAVY OIL BY STEAM INJECTION Filed Nov. 19, 1965 5Sheets-Sheet 4 ABDUS SATTER LLOYD E. ELKINS 1NVENTORS= BY ATTORNEY fe ljw; 295% 20% $2320 35E cow 9% com 08 8m 02 oo. 0m 0 m W. m 9m MEDZEQEE.ma W 0 M 1 3 m OOI|O 1 O 593 m 3 l 308 m w N 3 S 5 ow m 1 09 March 12,1968 RESERVOIR VOLUME A. SATTER ETAL 3,372,750

RECOVERY OF HEAVY OIL BY STEAM INJECTION Filed Nov. 19, 1965 5Sheets-Sheet 5 TEMPERATURE,F.

ABDUS SATTER LLOYD E. ELKINS INVENTORS:

BY W4 )V/n ATTORNEY United States Patent 3,372,750 RECOVERY OF HEAVY OILBY STEAM INJECTION Abdus Satter and Lloyd E. Ellrins, Tulsa, Okla,assignors to Pan American Petroleum Corporation, Tulsa, Okla,

a corporation of Delaware Filed Nov. 19, 1965, Ser. No. 508,791 Claims.(Cl. 166-11) ABSTRACT OF THE DISCLDSURE Steam is injected into anaquifer underlying a heavy oil reservoir to heat the reservoir andincrease production, primarily by decreasing viscosity. A single steaminjection-oil production well may be used along with a number ofsurrounding water-producing wells, or there may be a wellto-welldisplacement with one steam injection well, a set of surroundingwater-producing wells, and another set of surrounding oil producingwells, the two sets being respectively at the corners of the five-spotand at the midpoint of the border lines.

The present invention relates to the recovery of petroleum fromunderground deposits thereof by means of fluid drive. More particularly,it is concerned with, but not limited to, the recovery of petroleumhaving an API gravity of not more than about degrees, i.e., hereinafterreferred to as heavy oil, by steam injection under circumstances suchthat the steam not only serves as a drive agent to force oil into theproducting well but to lower the viscosity of the oil over a substantialportion thereof, thus aiding in increased production over a shortenedperiod of time.

In many areas of the world large deposits of petroleum exist which,because of their relatively low gravity, either cannot be produced orcan only be produced inefficiently by conventional methods. Suchdeposits include the Athabasca tar sands in Canada, low gravity crudesin the Iobo Field in Venezuela, and similar crudes in Western Missouri,Eastern Kansas and Southern Oklahoma. Numerous proposals have beenadvanced for recovering petroleum of the type contemplated herein, someof which have involved steam injection, in-place combustion, etc., butnone of them have met with unqualified success. for example, in the caseof steam injection procedures, a period of months is often required inorder to heat up a sufficiently large body of the oil before theaccompanying reduction in viscosity can be exploited. Also, in the nowwell-known hutf-and-puif process for recovering petroleum in which steamis injected into a well for a period of time after which thesteam-saturated formation is allowed to soak for an additional intervalprior to placing the well on production, much time elapses during whichno production is obtained. Also, the relative permeability of theformation to oil decreases owing to the increase in water saturation.

It is therefore an object of our invention to provide a process by whichheat can be applied to a large volume of the oil to be recovered whilesteam is simultaneously used to force the oil of reduced viscosity tothe well'. It is a particular object of our invention to provide amethod for recovering heavy oil from a formation adjacent a water sandin which the oil and water are separated for a distance of at least to50 feet from the well bore by a natural or artificial, substantiallyfluid-impermeable barrier. It is another object of our invention torecover heavy oil from a formation having a water zone above and/orbelow the oil producing zone, simultaneously injecting steam or hotwater into the oil and water zones,

and separately recovering oil and water from two or more Wells.

In the accompanying drawings,

FIGURE 1 is a diagrammatic representation of one embodiment of ourinvention having the wells arranged in a 5-spot pattern, the oil andwater zones penetrated by each steam injection well being separated byan artificial barrier.

FIGURE 2 represents a segment taken along line 22 of the pattern shownin FIGURE 1.

FIGURE 3 is another illustration showing a 9-spot arrangement having acentral steam injection Well and water and oil producing wells at thecorners and sides, respectively. 6

FIGURE 4 represents a segment taken along line 44 of the pattern shownin FIGURE 3.

FIGURE 5 illustrates still another arrangement of steam injection, oiland water producing wells.

FIGURE 6 represents a segment of the pattern shown in FIGURE 5 takenalong line 6-6.

FIGURE 7 is a plot showing the temperature distribution in anoil-bearing formationafter 349 days steam injection-due to conductionheating from water sand 10.

FIGURE 8 is another plot illustrating the percent of the oil reservoirsubjected to elevated temperature when the process of our invention isused.

In carrying out an embodiment of our invention, and referring first toFIGURES 1 and 2, we have the wells arranged in a 5spot pattern with thecentral well 8 producing water and steam condensate from aquifer orwater sand 10. Wells 12, stationed at each corner of the 5-spot, servethe dual purpose of steam injection and oil producing wells. Initially,the formation is fractured as nearly as possible between oil sand 9 andwater sand 10 after which cement is squeezed into the resulting openingto form a pancake or barrier 14 extending a substantial distance, i.e.,for at least 50 feet between wells 8 and 12. Thereafter packer 16carried on well tubing 18 is set opposite the cement-filled fracture sothat tubing 18 communicates only with water sand 10 via the perforations20 in casing 22. Steam is next introduced into water sand 10 via tubing18 and by condensing, transmits heat by conduction through concretebarrier 14- to reduce the viscosity of the oil in sand 9. Water in sand10, together with condensate, is removed from cased well 8 viaperformations 24. Energy transmitted to oil sand 9, through bypassing aportion of the injected steam around the end of barrier 14, plus gravitydrainage resulting from reduction in viscosity of the heavy oil, providesufficient force to cause oil to flow into well 12 through perforations26. Thus it is seen that energy required to cause oil to flow into well12 is not only derived from gravity drainage resulting from a reductionof oil viscosity but is also supplied through the use of steamdisplacement. In this way predominantly water-free oil is producedcontinuously and substantially immediately from well 12, unlike thehuffand-pufr" steam injection operation now widely employed. An increaseof rate of oil production is also obtained as the radius of the heatbank in oil-bearing sand 9 increases from the expansion of the steamzone in water sand 10. This method is versatile because it provides itsown barrier between the oil and water sands and does not necessarilyrequire the existence of a natural obstruction between the two sands.

After steam breakthrough occurs at water well 8, the rate of heatdissipation (due to conduction) from the steam-out water sand 10 intothe oil-bearing sand 9 decreases with the injection time since thethermal gradient around the water sand decreases with time. If steam isinjected at the original rate, the quality of steam produced increaseswith time and unnecessary loss of the injected heat results. We,therefore, propose that the steam injection rate be reduced with time,making sure that hot water essentially at the injected steam temperaturebe produced. Whether or not steam injection into the water-bearingformation should be continued or discontinued depends primarily upon theinjection rate, well spacing, and the thickness of the oil zone.

Temperatures and steam pressures employed may vary widely. However, oilsand injection temperatures usually are greater than those employed fortreatment of the adjacent water sand. Although the temperature and thequan tity of steam suitable for a given reservoir depends to some extenton the formation temperature and pressure, formation break-down pressureof the reservoir, and well spacing, we generally prefer to employ watersand steam injection rates of from about 3000 to about 40,000 lbs/hr. attemperatures of from about 300 to about 700 F. For the oil sand steaminjection, rates should ordinarily be somewhat lower than those used fortreatment of water sands. As a general rule, the steam pressure shouldexceed the formation pressure in either the oil or water sand by fromabout 50 to about 1000 p.s.i.but should not exceed the formationbreak-down pressure.

Referring again to the drawings, in FIGURES 3 and 4 we have a group ofwells arranged in a 9-spot pattern with injection well 28 located in thecenter and equipped with tubing 30 and packer 32, set substantially atthe oil-water interface 33. Cased corner wells 34 produce water fromsand 10 through perforations 35' while cased side wells 36 produce oiland water from oil sand 9. It is apparent in this connection that thefunction of wells 34 and 36 may be reversed, if desired. Steam isinjected into water sand 10 through tubing 30 and perforations 38 andinto oil sand 9 through the well annulus and perforations 40. Water andcondensate in sand 10 are produced from the various corner wells 34while oil plus some condensate are produced from sand 9 via perforations42 and side wells 36. Since a relatively thin section of water sand 10is used to inject steam at a many fold higher rate than that used ininjecting steam in oil sand 9, the water sand is steamed out much fasterthan the oil sand. This is also accentuated by the fact that the oilsand generally is much thicker than the water sand involved. After steambreakthrough occurs at water wells 34, steam injection into the watersand may be discontinued or the injection rate reduced as discussedbefore. If steam injection into water sand 10 is discontinued, thesurrounding water wells 34 may, if desired, be perforated and convertedinto oil producers.

Thus by following the procedure described immediately above inconnection with FIGURES 3 and 4, a major portion of the reservoir oilcan be heated to a higher temperature in a much shorter time so as toreduce its viscosity materially. Production of oil into wells 36 isconsiderably enhanced by simultaneous steam displacement in oil sand 9.In a straight oil displacement process (through the oil sand without thesimultaneous introduction of steam into an aquifer), the steam can bemoved through the oil sand only a relatively short distance from theinjection well. Although the temperature of the steam zone isessentially the same as that of the injected steam itself, the majorportion of the oil reservoir ahead of the steam zone remainssubstantially at the original reservoir temperature if steam injectioninto the aquifer is not used in accordance with our invention. Thus, thepresent invention makes possible the production of oil at a higher ratemuch sooner than can be accomplished by conventional well-to-well steamdisplacement processes or meth ods which first inject steam into anaquifer adjacent the oil zone to reduce the oil viscosity and thereafterproduce the oil by steam displacement.

In the case of the embodiment illsutrated in FIGURES and 6, another9-spot pattern is employed with central well 44 being a combinationsteam injection and oil producing well. Corner wells 46 are waterproducers while side wells 48 are steam injection wells. It iscontemplated that the function of cased wells 46 and 48 may be reversed.Prior to injection, steam via wells 44 and 48 and perforations 50 and52, respectively; packer 54 carried on well tubing 56, is setsubstantially opposite naturally occurring fluid impermeable barrier 58,e.g., from about 5 to 10 feet in thickness, which may be shale or otherequivalent material. Steam is then substantially simultaneously injectedinto oil sand 9 and water sand 10 through wells 48 and 44-,respectively. As the result of the wide and substantial distribution ofheat from water sand 10 through barrier 58, the oil in sand 9 is reducedin viscosity and is driven toward oil producing well 44 by energysupplied not only through gravity drainage but from steam displacementthrough the oil sand and via well 48. Recovery of oil flowing into well44 is effected through flow up the annulus thereof. After steambreakthrough occurs at water wells 46, steam injection into the watersand may be discontinued or the injection rate reduced as discussedbefore.

The method of our invention will be further illustrated by reference tothe following example:

Example In a 5-spot pattern similar to that shown in FIGURE 1, wells aredrilled through a 50-ft. oil-bearing zone and a 10-ft. thick water sandadjacent and directly beneath the oil-bearing zone. The reservoir has aninitial temperature and pressure of 70 F. and 650 p.s.i.g. Eightypercent quality steam is injected into the water zone through the cornerwells at a rate of 25,000 lbs/hr. at 800 p.s.i.a. and 518 F. Consideringa radial flow and a drainage area of 10 acres, approximately 349 daysare required to steam out the water-bearing zone. FIGURE 7 of thedrawings illustrates the temperature distributionby conduction of heatfrom the water zone--in the oil-bearing formation at the end of the349-day steam injection period. FIGURE 8 shows the percent of the oilreservoir (by volume) which is subjected to the elevated temperatures. Aconsiderable portion of the reservoir is heated to higher temperatures,for example, 37 percent of the volume of the reservoir attains thetemperature of 200 F.-an increase of 130 F. from the originaltemperature. It should be also noted that a rise of to 200 F. inreservoir temperature reduces the viscosity of heavy oilat the originalreservoir temperatureby a factor of 50 to several hundredfold.

As evident in the above illustration, at the time of steam breakthroughat the producing wells, a substantial part of the reservoir in the upperregion of the oil-bearing formation may not be heated sufficiently, orany at all, to be responsive to the proposed method of oil recovery. Inorder to heat the cooler portion of the reservoir, steam injection intothe water-bearing formation should be continued until a desired level oftemperature rise, e.g., 50 F. or above, in the entire oil-bearingformation is achieved. It the injection rate is higher and/or the wellspacing shorter than in the above example, the steam breakthrough timemay be shorter and the steam injection time after steam breakthrough maybe longer. Again, if the pay is thicker than, for example, 50 ft.,longer time of steam injection may be required after steam breakthroughthan is necessary in the case of the above example.

From the foregoing description it is apparent that we have provided theart with a novel, practical, and efiicient method for recoveringpetroleum, particularly that of the low-gravity type defined above. Byemploying the method of our invention, oil recovery response isimmediate as opposed to prior procedures requiring several months ofheating before such oil is obtained. Moreover, the process of ourinvention may be employed in the presence or absence of a natural orartificial barrier between the aquifer and the oil-bearing stratum.Also, by the use of our invention one can employ simultaneously, to bestadvantage for oil production, the combined forces of gravity drainageand steam displacement which we have shown to constitute a materialimprovement over the use of these two forces in sequence.

We claim:

1. In a process for recovering petroleum from an underground depositthereof penetrated by two wells, said deposit being adjacent awater-bearing zone, the improvement which comprises injecting steam downa first confined path in the first of said wells and into said waterzone thereby heating and reducing the viscosity of the petroleum in saiddeposit, simultaneously injecting steam down a first confined path inthe second of said wells and into said deposit, removing water from saidzone through a second confined path in the second of said wells andrecovering petroleum from said deposit through a second confined path inthe first of said wells.

2. The method of claim 1 in which steam injection is continued afterbreakthrough into the second of said wells until the temperature rise insubstantially the entire oilbearing formation is at least 50 F.

3. In a process for recovering petroleum from an underground depositthereof penetrated by three wells, said deposit being adjacent awater-bearing zone, the improvement which comprises injecting steam downa first confined path of the first of said Wells and into said waterbearing zone thereby heating and reducing the viscosity of the petroleumin said deposit, simultaneously injecting steam down the second of saidwells and into said deposit,

removing water from said zone via the third of said wells and recoveringpetroleum from said deposit through a second confined path in said firstwell.

4. In a process for recovering petroleum from an underground depositthereof penetrated by two wells, said 30 deposit being adjacent aWater-bearing zone, the improvement which comprises injecting steam downa first confined path in the first of said wells and into said waterzone thereby heating and reducing the viscosity of the petroleum in saiddeposit, simultaneously injecting steam down a second confined path insaid first well and then into said deposit, removing water from saidzone via a first confined path in said second well and recoveringpetroleum from said deposit via a second confined path in said secondwell.

5. In a process for recovering petroleum from an underground depositthereof penetrated by three wells, said deposit being adjacent awater-bearing zone, the improvement which comprises injecting steam downa first confined path of the first of said wells and into said waterbearing zone thereby heating and reducing the viscosity of the petroleumin said deposit, simultaneously injecting steam down a second confinedpath in said first well and into said deposit, removing water from saidzone via the second of said wells, and recovering petroleum from saiddeposit through the third of said wells.

References Cited UNITED STATES PATENTS 1,491,138 4/1924 HiXon 166-112,734,579 2/1956 Elkins 1661l 3,163,215 12/1964 Stratton 1661O 3,167,1201/1965 Pryor 16610 3,180,413 4/1965 Willman 166-11 3,251,413 5/1966Rudisell 166-10 STEPHEN 1. NOV OSAD, Primary Exan'ziner.

